Interspinous spacer

ABSTRACT

An implantable spacer for placement between adjacent spinous processes in a spinal motion segment is provided. The spacer includes a body defining a longitudinal axis and passageway. A first arm and a second arm are connected to the body. Each arm has a pair of extensions and a saddle defining a U-shaped configuration for seating a spinous process therein. Each arm has a proximal caming surface and is capable of rotation with respect to the body. An actuator assembly is disposed inside the passageway and connected to the body. When advanced, a threaded shaft of the actuator assembly contacts the caming surfaces of arms to rotate them from an undeployed configuration to a deployed configuration. In the deployed configuration, the distracted adjacent spinous processes are seated in the U-shaped portion of the arms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 60/958,876 entitled “Interspinous spacer”filed on Jul. 9, 2007 which is incorporated herein by reference in itsentirety. This application also claims priority to and is acontinuation-in-part of U.S. patent application Ser. No. 12/148,104filed entitled “Interspinous spacer” filed on Apr. 16, 2008 which claimspriority to and the benefit of U.S. Provisional Patent Application Ser.No. 60/923,971 entitled “Interspinous spacer” filed on Apr. 17, 2007 andU.S. Provisional Patent Application Ser. No. 60/923,841 entitled “Spacerinsertion instrument” filed on Apr. 16, 2007, all of which are herebyincorporated by reference in their entireties. This application is alsoa continuation-in-part of U.S. patent application Ser. No. 11/593,995entitled “Systems and methods for posterior dynamic stabilization of thespine” filed on Nov. 7, 2006 which is a continuation-in-part of U.S.patent application Ser. No. 11/582,874 entitled “Minimally invasivetooling for delivery of interspinous spacer” filed on Oct. 18, 2006which is a continuation-in-part of U.S. patent application Ser. No.11/314,712 entitled “Systems and methods for posterior dynamicstabilization of the spine” filed on Dec. 20, 2005 which is acontinuation-in-part of U.S. patent application Ser. No. 11/190,496entitled “Systems and methods for posterior dynamic stabilization of thespine” filed on Jul. 26, 2005 which is a continuation-in-part of U.S.patent application Ser. No. 11/079,006 entitled “Systems and methods forposterior dynamic stabilization of the spine” filed on Mar. 10, 2005which is a continuation-in-part of U.S. patent application Ser. No.11/052,002 entitled “Systems and methods for posterior dynamicstabilization of the spine” filed on Feb. 4, 2005 which is acontinuation-in-part of U.S. patent application Ser. No. 11/006,502entitled “Systems and methods for posterior dynamic stabilization of thespine” filed on Dec. 6, 2004 which is a continuation-in-part of U.S.patent application Ser. No. 10/970,843 entitled “Systems and methods forposterior dynamic stabilization of the spine” filed on Oct. 20, 2004,all of which are hereby incorporated by reference in their entireties.

FIELD

The present invention generally relates to medical devices, inparticular, implants for placement between adjacent spinous processes ofa patient's spine.

BACKGROUND

With spinal stenosis, the spinal canal narrows and pinches the spinalcord and nerves, causing pain in the back and legs. Typically, with age,a person's ligaments may thicken, intervertebral discs may deteriorateand facet joints may break down—all contributing to the condition of thespine characterized by a narrowing of the spinal canal. Injury,heredity, arthritis, changes in blood flow and other causes may alsocontribute to spinal stenosis.

Doctors have been at the forefront with various treatments of the spineincluding medications, surgical techniques and implantable devices thatalleviate and substantially reduce debilitating pain associated with theback. In one surgical technique, a spacer is implanted between adjacentinterspinous processes of a patient's spine. The implanted spacer opensthe spinal canal, maintains the desired distance between vertebral bodysegments, and as a result, avoids impingement of nerves and relievespain. For suitable candidates, an implantable interspinous spacer mayprovide significant benefits in terms of pain relief.

Any surgery is an ordeal. However, the type of device and how it isimplanted has an impact. For example, one consideration when performingsurgery to implant an interspinous spacer is the size of the incisionthat is required to allow introduction of the device. Small incisionsand minimally invasive techniques are generally preferred as they affectless tissue and result in speedier recovery times. As such, there is aneed for interspinous spacers that work well with surgical techniquesthat are minimally invasive for the patient. The present invention setsforth such a spacer.

SUMMARY

According to one aspect of the invention, an implantable spacer forplacement between adjacent spinous processes is disclosed. The implantincludes a body defining a longitudinal axis and passageway through atleast a portion of the body. A first arm and a second arm are bothconnected to the body and capable of rotation with respect to the body.Each arm defines a configuration suitable for cradling a spinousprocess. Each arm has a proximal caming surface. The spacer furtherincludes an actuator assembly connected to the body. The actuatorassembly comprises an actuator having at least one bearing surface and athreaded shaft connected to the actuator and configured for movementwith respect to the body. The actuator assembly is configured such thatthe actuator is disposed inside the body and configured to move relativeto the body such that the at least one bearing surface contacts thecaming surfaces of the arms to thereby rotate the arms from anundeployed configuration in which the arms are substantially parallel tothe longitudinal axis of the body to a deployed configuration in whichthe arms are substantially perpendicular to the longitudinal axis of thebody. The arms seat adjacent spinous processes when in the deployedconfiguration.

According to another aspect of the invention, an implantable spacer forplacement between adjacent spinous processes is disclosed. The spacerincludes a body defining a longitudinal axis and passageway through atleast a portion of the body. At least a first arm is connected to thebody and capable of movement with respect to the body and configured forreceiving a spinous process. The spacer further includes an actuatorconnected to the body, disposed inside the longitudinal passageway andconfigured to move relative to the body to deploy the at least first armfrom an undeployed configuration in which the first arm is substantiallyparallel to the longitudinal axis of the body to at least one deployedconfiguration in which the first arm is substantially perpendicular tothe longitudinal axis of the body. The first arm receives a spinousprocess when in the at least one deployed configuration.

According to another aspect of the invention, an implantable spacer forplacement between adjacent spinous processes is disclosed. The spacerincludes a body defining a longitudinal axis and passageway through atleast a portion of the body. A first arm and a second arm are connectedto the body and capable of rotation with respect to the body. Each armhas a pair of extensions and a saddle defining a configuration forseating a spinous process therein. Each arm has a proximal camingsurface. The spacer further includes an actuator connected to the bodyand configured to move relative to the body to deploy the arms from anundeployed configuration in which the arms are substantially parallel tothe longitudinal axis of the body to a deployed configuration in whichthe arms are substantially perpendicular to the longitudinal axis of thebody. The arms seat adjacent spinous processes when in the deployedconfiguration. The spacer further includes a retainer configured toretain the actuator inside the body while permitting the actuatorrelative movement with respect to the body.

According to another aspect of the invention, an implantable spacer forplacement between a superior spinous process and an adjacent inferiorspinous process is disclosed. The spacer includes a body defining alongitudinal axis and passageway through at least a portion of the body.At least a first arm is connected to the body and capable of movementwith respect to the body. The first arm has a configuration for seatingthe superior spinous process. The spacer further includes an actuatorconnected to the body, disposed inside the longitudinal passageway andconfigured to move relative to the body to deploy the at least first armfrom an undeployed configuration in which the first arm is substantiallyparallel to the longitudinal axis of the body to at least one deployedconfiguration in which the first arm is substantially perpendicular tothe longitudinal axis of the body. The first arm seats the superiorspinous process when in the at least one deployed configuration.

According to another aspect of the invention, a method for implanting aninterspinous spacer into a patient is disclosed. The method includes thestep of providing an implantable spacer configured for placement betweenadjacent spinous processes. The spacer includes a body having alongitudinal axis. The spacer further includes at least a first armconnected to the body and capable of movement with respect to the bodyand configured for receiving a spinous process. The spacer furtherincludes an actuator connected to the body and configured to moverelative to the body to deploy the at least first arm from an undeployedconfiguration in which the first arm is substantially parallel to thelongitudinal axis of the body to at least one deployed configuration inwhich the first arm is substantially perpendicular to the longitudinalaxis of the body. The first arm receives a spinous process when in theat least one deployed configuration. An incision is created in thepatient. The spacer is inserted through the incision to a targetedinterspinous process space between adjacent spinous processes. Theactuator is moved to move the at least first arm from an undeployedconfiguration to a first deployed configuration. The actuator is movedto move the at least first arm from the first deployed configuration toa second deployed configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.

FIG. 1 a illustrates a perspective view of a spacer according to thepresent invention.

FIG. 1 b illustrates a side view of a spacer according to the presentinvention.

FIG. 1 c illustrates a top view of a spacer according to the presentinvention.

FIG. 1 d illustrates a cross-sectional view of the spacer of FIG. 1 ctaken along line A-A according to the present invention.

FIG. 1 e illustrates an end view of a spacer according to the presentinvention.

FIG. 1 f illustrates an exploded perspective view of a spacer accordingto the present invention.

FIG. 2 a illustrates a perspective view of half of a body of a spaceraccording to the present invention.

FIG. 2 b illustrates a side view of half of a body of a spacer accordingto the present invention.

FIG. 2 c illustrates a perspective view of another half of a body of aspacer according to the present invention.

FIG. 2 d illustrates a side view of the other half of a body of a spaceraccording to the present invention.

FIG. 3 a illustrates a perspective view of a superior arm of a spaceraccording to the present invention.

FIG. 3 b illustrates a back view of a superior arm of a spacer accordingto the present invention.

FIG. 3 c illustrates a side view of a superior arm of a spacer accordingto the present invention.

FIG. 3 d illustrates a perspective view of an inferior arm of a spaceraccording to the present invention.

FIG. 3 e illustrates a back view of an inferior arm of a spaceraccording to the present invention.

FIG. 3 f illustrates a side view of an inferior arm of a spaceraccording to the present invention.

FIG. 4 a illustrates a perspective view of a half of a body and actuatorassembly of a spacer according to the present invention.

FIG. 4 b illustrates a side view of a portion of a half of a body andactuator assembly of a spacer according to the present invention.

FIG. 5 a illustrates a side view of a spacer in a closed, undeployedconfiguration according to the present invention.

FIG. 5 b illustrates a side view of a spacer in a partially deployedconfiguration according to the present invention.

FIG. 5 c illustrates a side view of a spacer in a deployed configurationaccording to the present invention.

FIG. 5 d illustrates a side view of a spacer in a deployed and extendedconfiguration according to the present invention.

FIG. 6 a illustrates a side, cross-sectional view of a spacer in apartially deployed configuration according to the present invention.

FIG. 6 b illustrates a side, cross-sectional view of a spacer in adeployed configuration according to the present invention.

FIG. 6 c illustrates a side, cross-sectional view of a spacer in adeployed and extended configuration according to the present invention.

FIG. 7 a illustrates a side, semi-transparent view of a spacer in apartially deployed configuration according to the present invention.

FIG. 7 b illustrates a side, semi-transparent view of a spacer in adeployed configuration according to the present invention.

FIG. 7 c illustrates a side, semi-transparent view of a spacer in adeployed and extended configuration according to the present invention.

FIG. 8 a illustrates a perspective view of a spacer according to thepresent invention.

FIG. 8 b illustrates a side view of a spacer according to the presentinvention.

FIG. 8 c illustrates a top view of a spacer according to the presentinvention.

FIG. 8 d illustrates a cross-sectional view of the spacer of FIG. 8 ctaken along line A-A according to the present invention.

FIG. 8 e illustrates an end view of a spacer according to the presentinvention.

FIG. 8 f illustrates an exploded perspective view of a spacer accordingto the present invention.

FIG. 9 a illustrates a perspective view of half of a body of a spaceraccording to the present invention.

FIG. 9 b illustrates a side view of half of a body of a spacer accordingto the present invention.

FIG. 10 a illustrates a perspective view of a superior arm of a spaceraccording to the present invention.

FIG. 10 b illustrates a back view of a superior arm of a spaceraccording to the present invention.

FIG. 10 c illustrates a side view of a superior arm of a spaceraccording to the present invention.

FIG. 10 d illustrates a perspective view of an inferior arm of a spaceraccording to the present invention.

FIG. 10 e illustrates a back view of an inferior arm of a spaceraccording to the present invention.

FIG. 10 f illustrates a side view of an inferior arm of a spaceraccording to the present invention.

FIG. 11 a illustrates a perspective view of a half of an actuator shaftand retainer of a spacer according to the present invention.

FIG. 11 b illustrates a side view of a portion of an actuator shaft andretainer of a spacer according to the present invention.

FIG. 12 a illustrates a side view of a spacer in a closed, undeployedconfiguration according to the present invention.

FIG. 12 b illustrates a side view of a spacer in a partially deployedconfiguration according to the present invention.

FIG. 12 c illustrates a side view of a spacer in a deployedconfiguration according to the present invention.

FIG. 12 d illustrates a side view of a spacer in a deployed and extendedconfiguration according to the present invention

FIG. 13 a illustrates a side, cross-sectional view of a spacer in apartially deployed configuration according to the present invention.

FIG. 13 b illustrates a side, cross-sectional view of a spacer in adeployed configuration according to the present invention.

FIG. 13 c illustrates a side, cross-sectional view of a spacer in adeployed and extended configuration according to the present invention.

FIG. 14 a illustrates a side, semi-transparent view of a spacer in apartially deployed configuration according to the present invention.

FIG. 14 b illustrates a side, semi-transparent view of a spacer in adeployed configuration according to the present invention.

FIG. 14 c illustrates a side, semi-transparent view of a spacer in adeployed and extended configuration according to the present invention.

FIG. 15 a illustrates a side view of an insertion instrument connectedto a spacer in a closed, undeployed configuration according to thepresent invention.

FIG. 15 b illustrates a side view of an insertion instrument connectedto a spacer in a partially deployed configuration according to thepresent invention.

FIG. 15 c illustrates a side view of an insertion instrument connectedto a spacer in a deployed configuration according to the presentinvention.

FIG. 15 d illustrates a side view of an insertion instrument connectedto a spacer in a deployed and extended configuration according to thepresent invention.

FIG. 16 illustrates a spacer according to the present invention deployedin an interspinous process space between two vertebral bodies and asupraspinous ligament.

DETAILED DESCRIPTION

Before the subject devices, systems and methods are described, it is tobe understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “aspinal segment” may include a plurality of such spinal segments andreference to “the screw” includes reference to one or more screws andequivalents thereof known to those skilled in the art, and so forth.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates which may need to beindependently confirmed.

The present invention is described in the accompanying figures and textas understood by a person having ordinary skill in the field of spinalimplants and implant delivery instrumentation.

With reference to FIGS. 1 a -1 f, various views of a spacer 10 accordingto the present invention are shown. The spacer 10 includes a body 12connected to a superior extension member or arm 14, an inferiorextension member or arm 16, and an actuator assembly 18.

Turning now to FIGS. 2 a -2 d, the body 12 will now be described. Thebody 12 is shown to have a clamshell construction with a left body piece20 (shown in FIGS. 2 a and 2 b ) joined to a right body piece 22 (shownin FIGS. 2 c and 2 d ) to capture arms 14, 16 inside. With the right andleft body pieces 20, 22 joined together, the body 12 is generallycylindrical. It has a cross-sectional size and shape that allows forimplantation between adjacent spinous processes and facilitates deliveryinto a patient through a narrow port or cannula.

The inside of the body 12 defines an arm receiving portion 24 and anactuator assembly receiving portion 26 with features formed in each ofthe left and right body pieces 20, 22 that together define the arm andactuator assembly receiving portions 24, 26. In one variation, the armreceiving portion 24 includes slots or openings 28 that receive pinsformed on the arms 14, 16 such that the pins rotate and/or translateinside the openings 28. The actuator assembly receiving portion 26includes a threaded passageway 30. Other features include a tongue andgroove for mating with the opposite clamshell.

The outside of the body 12 defines a ledge 32 along at least a portionof the periphery. Notches 34 are formed at opposite locations as alsoshown in FIG. 1B. The notches 34 are configured for pronged attachmentto a spacer delivery instrument. When joined together, the left andright body pieces 20, 22 define a proximal opening 36 (as seen in FIG. 1e ) and a distal opening 38 (as seen in FIG. 1 a ) in the body 12. Alongitudinal scallop (not shown) extending from the proximal end of thespacer to the distal end is formed in the outer surface of the body 12to facilitate placement of the spacer 10 between and to conform to theanatomy of adjacent interspinous processes.

Turning now to FIGS. 3 a -3 c, the superior arm 14 is shown and in FIGS.3 d -3 f, the inferior arm 16 is shown. The superior and inferior arms14, 16 include pins 40 for mating with the body 12, in particular, formating with the slots/openings 28 of the arm receiving portion 24. Eachof the superior and inferior arms 14, 16 includes at least one camingsurface 41, 43, respectively, for contact with the actuator assembly 18.The superior and inferior arms 14, 16 include elongated superiorextensions 42 a, 42 b and elongated inferior extensions 44 a, 44 b,respectively. Extensions 42 a and 44 a are located on the left adjacentto the left body piece 20 and extensions 42 b and 44 b are located onright adjacent to the right body piece 22. Superior extensions 42 a, 42b extend substantially parallel to each other in both an undeployedconfiguration and in a deployed configuration as do inferior extensions44 a, 44 b. Extending between extensions 42 a, 42 b is a strut, bridge,bracket or saddle 46 that forms a superior substantially U-shapedconfiguration that is sized and configured to receive a superior spinousprocess. As seen in FIG. 3 c , the anterior face of the superiorextensions 14 includes a slight concavity or curvature 45 for conformingto the bony anatomy of the superior spinous process and or lamina. Also,extending between inferior extensions 44 a, 44 b is a strut, bridge,bracket or saddle 48 that forms an inferior substantially U-shapedconfiguration together with the extensions 44 a, 44 b that is sized andconfigured to receive an inferior spinous process of a spinal motionsegment. As seen in FIG. 3 f , the anterior face of the inferiorextensions 16 includes a slight convexity or curvature 47 for conformingto the bony anatomy of the inferior spinous process and/or lamina.

The superior and inferior arms 14, 16 are movably or rotatably connectedto the body 12, for example by hinge means or the like to providerotational movement from an undeployed configuration to a deployedconfiguration that arcs through about a 90 degree range or more withrespect to the body 12. The arms 14, 16 are rotationally movable betweenat least an undeployed, collapsed or folded state (as shown in FIGS. 1a-1 e ) and at least one deployed state (as shown in FIGS. 5 c, 5 d, 6b, 6 c, 7 b, and 7 c ). In the undeployed state, the arm pairs 14, 16are aligned generally or substantially axially (i.e., axially with thelongitudinal axis, defined by the body 12 or to the translation pathinto the interspinous space of the patient) to provide a minimal lateralor radial profile. The longitudinal axis X of the spacer and body isshown in FIG. 1 c. In the deployed state, the arm pairs 14, 16 arepositioned such that each of the U-shaped saddles are in a plane (orplanes) or have a U-shaped projection in a plane that is (are) generallyor substantially transverse to the longitudinal axis X defined by thebody 12 or to the collapsed position or to the implantation path intothe interspinous space of the patient. In one variation, the spacer 10is configured such the arms 14, 16 are linearly moveable or translatablewithin the plane from a first deployed state (such as the state shown inFIGS. 5 c, 6 b and 7 b ) to and from a second deployed state (such asthe state shown in FIGS. 5 d, 6 c and 7 c ) characterized by anadditional translation of at least one of the arms 14, 16 with respectto the body 12 along a direction of the arrows as shown in FIG. 7 c .More specifically, the arms 14, 16 can be extended in the generalvertical direction along an axis along the general length the spinewherein the arms 14, 16 are extended away from each other and away fromthe body 12 as denoted by the arrows in FIG. 7 c . This featureadvantageously allows for the most minimally invasive configuration forthe spacer without compromising the ability of the spacer 10 to seat andcontain the spinous processes in between levels where the anatomy of thespinous processes is such that the interspinous process space increasesin the anterior direction or without compromising the ability of thespacer to provide adequate distraction. The arms 14, 16 are connected tothe body 12 and/or to each other in a manner that enables them to bemoved simultaneously or independently of each other, as well as in amanner that provides passive deployment and/or vertical extension or,alternatively, active or actuated deployment and/or vertical extension.

Turning back to FIG. 1 f, the actuator assembly 18 will now bedescribed. The actuator assembly 18 includes an actuator 48 connected toa shaft 50 and retainer 52. The actuator 48 includes a distal end 54 anda proximal end 56 and at least two bearing surfaces 58. The bearingsurfaces 58 angle towards each other from the proximal end 54 to thedistal end 56. The proximal end 54 of the actuator 48 includes a shaftreceiving portion 60 configured to receive the shaft 50. The distal endof the actuator 48 is further configured to engage the superior andinferior arms 14, 16 such that forward translation of the actuator 48relative to the body 12 effects deployment of the arms into at least onedeployed configuration.

Still referencing FIG. 1 f , the shaft 50 is substantially cylindricalin shape and includes a threaded outer surface for engagement with thethreaded inner surface of the actuator assembly receiving portion 26 ofthe body 12. The threads on the inner surface of the body 12 are formedby the conjunction of both left and right body pieces 20, 22. Theproximal end of the shaft 50 includes a hex socket 62 for receiving adriving tool for advancing the actuator assembly 18 with respect to thebody 12. The distal end of the shaft 50 includes an actuator engagementportion 64 configured to connect to the actuator 48. The actuatorengagement portion 64, as shown in FIG. 1 f, is a projection that slidesinto a channel 66 on the actuator 48. Once inserted into the channel 66,movement of the shaft 50 solely along the longitudinal axis of thespacer 10 will not release the shaft 50 from the actuator 48. In onevariation, the actuator 48 and shaft 50 are integrally formed.

Still referencing FIG. 1 f, the retainer 52 is a circular ringpreferably made of metal such as surgical steel or titanium. Theretainer 52 fits into a recess 68 formed on the inner surface of thebody 12. When pressed into the recess 68, the retainer 52 secures theactuator 48 inside the passageway 30 of the body 12. The actuatorassembly 18 is at least partially disposed inside the body 12 and isconfigured for sliding engagement with respect to the body 12.

Assembly of the spacer 10 with reference to FIGS. 1 a-1 f will now bedescribed. The arms 14, 16 are disposed in the arm receiving portion 24of one body piece. The other of the left or right body piece 20, 22 issecurely connected/welded to the one body piece thereby capturing thearms 14, 16 inside the arm receiving portion 24 such that the arms 14,16 are capable of at least rotational movement with respect to the body12 and in one variation, capable of rotational movement and translationwith respect to the body 12. In a variation in which the body 12 is madeof one piece, the arms 14, 16 are movably connected to the body 12 witha pin. The shaft 50 is connected to the actuator 48 and togetherinserted and threadingly connected into the passageway 30 of the body12. The retainer 52 is passed over the proximal end of the shaft 50 andsnapped into the recess 68 of the body 12 to secure the actuatorassembly 18 inside the body 12 such that the actuator assembly 18 iscapable of threaded translational movement with respect to the body 12.

With particular reference to FIGS. 4 a and 4 b , in one variation, thethreaded shaft 50 contacts the threaded inner surface of the body 12 inan interference fit engagement wherein the inner diameter of the bodythreads is smaller than the root diameter of the shaft threads as shownin FIG. 4 b . This interference helps prevent the shaft 50 fromloosening and backing-up out of the body 12 which would result infolding of the arms 14, 16. The interference is created with the threadsof the shaft 50 and one or more of the distally located threads alongthe body 12 such that when advancement of the shaft 50 nears completedeployment (at approximately 90 degrees splaying of the arms 14, 16 withrespect to the body 12) the distally located “interference” threads areengaged to tighten the shaft 50 to the body 12, thereby, providing aninterference lock which is reversible by turning the shaft in theopposite direction. The interference lock with one or more of thedistally located threads affords the surgeon flexibility in that thespacer 10 can be partially deployed and undeployed (via rotation of theshaft 50 in the opposite direction) repeatedly until the surgeon locatesand properly seats the implant before locking it by advancing the shaftfurther into the section of the threads where the interference fit iscreated.

Referring now to FIGS. 5 a -5 d, the spacer 10 is shown in a closed,undeployed configuration (FIG. 5 a ), a partially deployed configurationor otherwise intermediary configuration (FIG. 5 b ), a deployedconfiguration (FIG. 5 c ), and a deployed and extended configuration(FIG. 5 d ). In moving from an undeployed to a deployed configuration,the actuator assembly 18, and in particular, the shaft 50 of theactuator assembly moves distally with respect to the body 12 and theshaft 50 advantageously moves to a position flush with the proximal endof the body 12 or to a position completely inside the body 12disappearing from sight providing a low profile for the spacer 10 alongthe longitudinal axis of the body 12.

Turning now to the cross-sectional views of the spacer 10 in FIGS. 6 a-6 c, as the shaft 50 advances within the passageway 30, the bearingsurfaces 58 of the actuator 48 contact the superior and inferior camingsurfaces 41, 43 of the superior and inferior arms 14, 16 turning thearms 14, 16 into rotation with respect to the body 12. Upon rotation,the bearing surfaces 58 of the actuator 48 slide with respect to thesuperior and inferior caming surfaces 41, 43 of the superior andinferior arms 14, 16. The arms 14, 16 rotate through an arc ofapproximately 90 degrees with respect to the body 12 into the deployedconfiguration (FIG. 6 b ) and with further actuation, into a deployedand extended configuration (FIG. 6 c ) in which the superior andinferior extensions of the arms 14, 16 are substantially perpendicularto the longitudinal axis of the spacer 10 as shown in FIGS. 6 b and 6 c.

Turning now to the semi-transparent views of the spacer 10 in FIGS. 7 a-7 c, the rotation of the pins 40 of the arms 14, 16 in the slots 28 ofthe body 12 is shown in moving from the configuration of FIG. 7 a to theconfiguration of FIG. 7 b . The translation of the pins 40 of the arms14, 16 in the elongated portion of the slots 28 of the body 12 is shownin moving from the deployed configuration of FIG. 7 b to the deployedand extended configuration of FIG. 7 c in the direction of the arrows inFIG. 7 c . Such outward translation with respect to the body 12 isguided by the length and shape of the slots 28. Reverse rotation of theshaft 50 moves the shaft 50 proximally with respect to the body 12allowing the arms to close to any intermediary configuration between adeployed, extended configuration and an undeployed, closedconfiguration. This feature advantageously permits the surgeon to easeinstallation and positioning of the spacer with respect to patientanatomy.

With reference to FIGS. 8 a -8 f, various views of another variation ofa spacer 10 according to the present invention are shown wherein likereference numbers are used to describe like parts. The spacer 10includes a body 12 connected to a superior extension member or arm 14,an inferior extension member or arm 16, and an actuator assembly 18.

Turning now to FIGS. 9 a and 9 b , the body 12 will now be described.The body 12 is shown to have a clamshell construction with a left bodypiece 20 (shown in FIG. 9 a ) joined to a right body piece 22 (shown inFIG. 9 b ) to capture arms 14, 16 inside. With the right and left bodypieces 20, 22 joined together, the body 12 is generally cylindrical. Ithas a cross-sectional size and shape that allows for implantationbetween adjacent spinous processes and facilitates delivery into apatient through a narrow port or cannula.

The inside of the body 12 defines an arm receiving portion 24 and anactuator assembly receiving portion 26 with features formed in each ofthe left and right body pieces 20, 22 that together define the arm andactuator assembly receiving portions 24, 26. In one variation, the armreceiving portion 24 includes slots or openings or apertures 28 thatreceive pins formed on the arms 14, 16 such that the pins rotate and/ortranslate inside the slots or apertures 28. The actuator assemblyreceiving portion 26 includes a passageway 30. Other features include atongue and groove for mating with the opposite clamshell.

The outside of the body 12 defines a ledge 32 along at least a portionof the periphery. Notches 34 are formed at opposite locations as alsoshown in FIG. 8 b . The notches 34 are configured for pronged attachmentto a spacer delivery instrument. When joined together, the left andright body pieces 20, 22 define a proximal opening 36 (as seen in FIG. 8e ) and a distal opening 38 (as seen in FIG. 8 a ) in the body 12. Alongitudinal scallop (not shown) extending from the proximal end of thespacer to the distal end is formed in the outer surface of the body 12to facilitate placement of the spacer 10 between and to conform to theanatomy of adjacent interspinous processes.

Turning now to FIGS. 10 a -10 c, the superior arm 14 is shown and inFIGS. 10 d -10 f, the inferior arm 16 is shown. The superior andinferior arms 14, 16, include pins 40 for mating with the body 12, inparticular, for mating with the slots or apertures 28 of the armreceiving portion 24. Each of the superior and inferior arms 14, 16includes at least one caming surface 41, 43, respectively, for contactwith the actuator assembly 18. The superior and inferior arms 14, 16include elongated superior extensions 42 a, 42 b and elongated inferiorextensions 44 a, 44 b, respectively. Extensions 42 a and 44 a arelocated on the left adjacent to the left body piece 20 and extensions 42b and 44 b are located on right adjacent to the right body piece 22.Superior extensions 42 a, 42 b extend substantially parallel to eachother in both an undeployed configuration and in a deployedconfiguration as do inferior extensions 44 a, 44 b. Extending betweenextensions 42 a, 42 b is a strut, bridge, bracket or saddle 46 thatforms a superior substantially U-shaped configuration that is sized andconfigured to receive a superior spinous process. As seen in FIG. 10 c ,the anterior face of the superior extensions 14 includes a slightconcavity or curvature 45 for conforming to the bony anatomy of thesuperior spinous process and or lamina. Also, extending between inferiorextensions 44 a, 44 b is a strut, bridge, bracket or saddle 48 thatforms an inferior substantially U-shaped configuration together with theextensions 44 a, 44 b that is sized and configured to receive aninferior spinous process of a spinal motion segment. As seen in FIG. 10f , the anterior face of the inferior extensions 16 includes a slightconvexity or curvature 47 for conforming to the bony anatomy of theinferior spinous process and or lamina.

The superior and inferior arms 14, 16 are movably or rotatably connectedto the body 12, for example by hinge means or the like to providerotational movement from an undeployed configuration to a deployedconfiguration in which the arms arc through about a 90 degree range ormore with respect to the body 12. The arms 14, 16 are rotationallymovable between at least an undeployed, collapsed or folded state (asshown in FIGS. 8 a-8 e ) and at least one deployed state (as shown inFIGS. 12 c, 12 d, 13 b, 13 c, 14 b and 14 c ). In the undeployed state,the arm pairs 14, 16 are aligned generally or substantially axially(i.e., axially with the longitudinal axis defined by the body 12 or tothe translation path into the interspinous space of the patient) toprovide a minimal lateral or radial profile. The longitudinal axis X ofthe spacer and body is shown in FIG. 8 c . In the deployed state, thearm pairs 14, 16 are positioned such that each of the U-shaped saddlesare in a plane(s) or have a U-shaped projection in a plane that isgenerally or substantially transverse to the longitudinal axis X definedby the body 12 or to the collapsed position or to the implantation pathinto the interspinous space of the patient. In one variation, the spacer10 is configured such the arms 14, 16 are linearly moveable ortranslatable within the plane from a first deployed state (such as thestate shown in FIGS. 12 c, 13 b, 14 b ) to and from a second deployedstate (such as the state shown in FIG. 12 d, 13 c, 14 c ) characterizedby an additional translation of at least one of the arms 14, 16 withrespect to the body 12 along a direction of the arrows as shown in FIG.14 c . More specifically, the arms 14, 16 can be extended in the generalvertical direction along an axis substantially parallel to the spinewherein the arms 14, 16 are extended away from each other and away fromthe body 12 as denoted by the arrows in FIG. 14 c . This featureadvantageously allows for the most minimally invasive configuration forthe spacer without compromising the ability of the spacer 10 to seat andcontain the spinous processes in between levels where the anatomy of thespinous processes is such that the interspinous process space increasesin the anterior direction or without compromising the ability of thespacer to provide adequate distraction. The arms 14, 16 are connected tothe body 12 and/or to each other in a manner that enables them to bemoved simultaneously or independently of each other, as well as in amanner that provides passive deployment and/or vertical extension or,alternatively, active or actuated deployment and/or vertical extension.

Turning back to FIG. 8 f , the actuator assembly 18 will now bedescribed. The actuator assembly 18 includes an actuator 48 connected toa shaft 50 and retainer 52. The actuator 48 includes a distal end 54 anda proximal end 56 and at least two bearing surfaces 58. The bearingsurfaces 58 angle towards each other from the proximal end 54 towardsthe distal end 56. The proximal end 54 of the actuator 48 includes ashaft receiving portion 60 configured to receive the shaft 50. Thedistal end of the actuator 48 is further configured to engage thesuperior and inferior arms 14, 16 such that forward translation of theactuator 48 relative to the body 12 effects deployment of the arms intoat least one deployed configuration.

Still referencing FIG. 8 f , the shaft 50 is substantially cylindricalin shape and includes a threaded outer surface for engagement with athreaded inner surface of the retainer 52. The proximal end of the shaft50 includes a hex socket 62 for receiving a driving tool for advancingthe actuator assembly 18 with respect to the body 12 to deploy the arms14, 16. The distal end of the shaft 50 includes an actuator engagementportion 64 configured to connect to the actuator 48. The actuatorengagement portion 64 as shown in FIG. 8 f , is a projection that slidesinto a channel 66 on the actuator 48. Once inserted into the channel 66,movement of the shaft 50 solely along the longitudinal axis of thespacer 10 will not release the shaft 50 from the actuator 48. In onevariation, the actuator 58 and shaft 50 are integrally formed.

Still referencing FIG. 8 f , the retainer 52, which is preferably madeof metal such as surgical steel or titanium, includes a circularproximal end 70 and two prongs 72 extending distally from the circularproximal end 70 configured to received the shaft 50. Clearance for thepassage of the actuator 48 is provided between the prongs 72. Threadsare formed on the inner surface of the prongs 72 for conformalengagement with the threads on the shaft 50 such that the shaft 50 maythreadingly pass through the retainer 52. In one variation each prong 72is split down the middle as shown in FIG. 8 f . A ledge 74 is formedalong at least a portion of the periphery of the retainer 52 at theproximal end. The ledge 74 of the retainer 52 fits into a recess 68formed on the inner surface of the body 12. When pressed into the recess68, the retainer 52 is secured to the body 12 and the retainer 52 inturn secures the actuator 48 inside the passageway 30 of the body 12.Alignment flats 76 are formed at locations opposite to each other on theouter surface of the retainer 52. The alignment flats 76 keep thethreaded insert aligned with the body 12.

Assembly of the spacer 10 with reference to FIG. 8 f will now bedescribed. The arms 14, 16 are disposed in the arm receiving portion 24of one body piece. The other of the left or right body piece 20, 22 issecurely connected/welded to the one body piece thereby capturing thearms 14, 16 inside the arm receiving portion 24 such that the arms 14,16 are capable of rotational movement with respect to the body 12 and,in one variation, capable of rotational movement and translation withrespect to the body 12. The shaft 50 threaded into the retainer 52 andconnected to the actuator 58. The retainer 52 and the actuator 48 andshaft 50 are inserted into the passageway 30 of the body 12 and theretainer 52 is snapped inside the recess 68 of the body 12 to secure theactuator 48 inside the body 12 such that the actuator assembly 18 iscapable of threaded translational movement with respect to the body 12.

With particular reference to FIGS. 11 a and 11 b , the threaded shaft 50contacts the threaded inner surface of the retainer 52 in aninterference fit engagement wherein the inner diameter of the retainerthreads is smaller than the root diameter of the shaft threads as shownin FIG. 11 b. This interference helps prevent the shaft 50 fromloosening and backing-up out of the body 12 which would result infolding of the arms 14, 16. The interference is created with the threadsof the shaft 50 and one or more of the threads along the retainer 52such that when advancement of the shaft 50 nears complete deployment (atapproximately 90 degrees splaying of the arms 14, 16 with respect to thebody 12) the distally located “interference” threads relative to themore proximally located non-interference threads of the same retainer 52are engaged to tighten the shaft 50 to the retainer 52 and in turn tothe body 12, thereby, providing an interference lock which is reversibleby turning the shaft in the opposite direction. The prongs 72 of theretainer 52 advantageously and reversibly flex outwardly and inwardlyinstead of plastically deforming. This feature allows the implant to berepeatedly locked and unlocked without wearing out the threads andthereby preserving the interference lock feature. The interference lockwith one or more of the distally located threads affords the surgeonflexibility in that the spacer 10 can be partially deployed andundeployed (via rotation of the shaft 50 in the opposite direction)repeatedly until the surgeon locates and properly seats the implantbefore locking it by advancing the shaft further into the section of thethreads where the interference fit is created.

Referring now to FIGS. 12 a -12 d, the spacer 10 is shown in a closed,undeployed configuration (FIG. 12 a ), a partially deployedconfiguration, or intermediary configuration (FIG. 12 b ), a deployedconfiguration (FIG. 12 c ), and a deployed and extended configuration(FIG. 12 d ). In moving from an undeployed to a deployed configuration,the actuator assembly 18, and in particular, the shaft 50 of theactuator assembly moves distally with respect to the body 12 and theshaft 50 advantageously moves to a position flush with the proximal endof the body 12 or to a position completely inside the body 12disappearing from sight providing a low profile for the spacer 10 alongthe longitudinal axis of the body 12.

Turning now to the cross-sectional views of the spacer 10 in FIGS. 13 a-13 c, as the shaft 50 advances within the passageway 30, the bearingsurfaces 58 of the actuator 48 contact the superior and inferior camingsurfaces 41, 43 of the superior and inferior arms 14, 16 turning thearms 14, 16 into rotation with respect to the body 12. Upon rotation,the bearing surfaces 58 of the actuator 48 slide with respect to thesuperior and inferior caming surfaces 41, 43 of the superior andinferior arms 14, 16. The arms 14, 16 rotate through an arc ofapproximately 90 degrees with respect to the body 12 into the deployedconfiguration (FIG. 13 b ) and with further actuation, into a deployedand extended configuration (FIG. 13 c ) in which the superior andinferior extensions of the arms 14, 16 are substantially perpendicularto the longitudinal axis of the spacer 10 as shown in FIGS. 13 b and 13c.

Turning now to the semi-transparent views of the spacer 10 in FIGS. 14 a-14 c, the rotation of the pins 40 of the arms 14, 16 in the slots 28 ofthe body 12 is shown in moving from the configuration of FIG. 14 a tothe configuration of FIG. 14 b . The translation of the pins 40 of thearms 14, 16 in the elongated portion of the slots 28 of the body 12 isshown in moving from the deployed configuration of FIG. 14 b to thedeployed and extended configuration of FIG. 14 c in the direction of thearrows in FIG. 14 c . Such outward translation with respect to the body12 is guided by the length and shape of the slots 28. Reverse rotationof the shaft 50 moves the shaft 50 proximally with respect to the body12 allowing the arms to close to any intermediary configuration betweena deployed, extended configuration and an undeployed, closedconfiguration. This feature advantageously permits the surgeon to easeinstallation and positioning of the spacer with respect to patientanatomy.

The spacer of FIGS. 8-14 is delivered and deployed in the same manner asthe spacer of FIGS. 1-7 . To deliver and deploy the spacer 10 within thepatient, the spacer 10 is releasably attached to an insertion instrument80 at the proximal end of the spacer 10 via notches 34. The insertioninstrument 80 includes a first assembly 102 connected to a secondassembly 104 and a handle assembly 106.

The spacer 10 is provided or otherwise placed in its undeployed, closedstate in juxtaposition to the insertion instrument 80 and connectedthereto as shown in FIG. 15 a . The longitudinal axis of the insertioninstrument 80 is advantageously substantially aligned with thelongitudinal axis of the spacer 10 as shown. The delivery instrument 80includes a first subassembly 102 to releasably clamp to the body 12 ofthe spacer 10 at a distal end of the insertion instrument 80. The firstsubassembly 102 includes an inner clamp shaft (not shown) havingflexible prongs 126 at the distal end configured for attachment to thebody 12 of the spacer 10 and, in particular, for insertion into thenotches 34 of the spacer body 12. The first subassembly 102 includes anouter shaft 112 located over the inner clamp shaft and configured forrelative motion with respect to one another via a control 114 located atthe handle assembly 106. The control 114 is threaded to the outer shaft112 such that rotation of the control 114 moves the outer shaft 112along the longitudinal axis of the insertion instrument 80 over theinner clamp shaft to deflect and undeflect the prongs 126 to connect ordisconnect the instrument 80 to or from the body 12. The first control114 is activated at the handle of the insertion instrument 100 such thatthe first subassembly 102 is connected to the body 12 of the spacer 10.The first control 114 is rotated in one direction to advance the outershaft 112 over the inner clamp shaft 110 deflecting the prongs 118inwardly into the notches 34 on the body of the spacer 12 to secure thespacer body 12 to the instrument as shown clearly in FIG. 15 a . Reverserotation of the control 114 reverses the direction of translation of theouter shaft 112 to release the prongs 126 from the notches 34 and,thereby, release the spacer 10 from the instrument 80.

Still referencing FIG. 15 a , the insertion instrument 80 includes asecond subassembly 104 that is configured to connect to the actuatorassembly 18 of the spacer 12. In particular, the second subassembly 104includes means located at the distal end of the second subassembly 104to activate the actuator assembly 18. In one variation, the secondsubassembly 104 is a hexagonal-shaped driver having an elongated shaftthat is configured to be insertable into the hex socket 62 of the shaft50 while the spacer 10 is connected to the instrument 80. The secondsubassembly 104 is insertable at the proximal end of the instrument 80and extends through the handle assembly 106 and through the inner shaft.The removable driver 104 is rotatable with respect to the instrument 80to arrange the spacer 10 to and from deployed and undeployedconfigurations.

To deliver and deploy the spacer 10 within the patient, the spacer 10 isreleasably attached to a delivery instrument 80 at the proximal end ofthe spacer 10 as described. A small midline or lateral-to-midlineincision is made in the patient for minimally-invasive percutaneousdelivery. In one variation, the supraspinous ligament is splitlongitudinally along the direction of the tissue fibers to create anopening for the instrument. Dilators may be further employed to createthe opening. In the undeployed state with the arms 14, 16 in a closedorientation and attached to a delivery instrument, the spacer 10 isinserted into a port or cannula, if one is employed, which has beenoperatively positioned to an interspinous space within a patient's backand the spacer is passed through the cannula to the interspinous spacebetween two adjacent vertebral bodies. The spacer 10 is advanced beyondthe end of the cannula or, alternatively, the cannula is pulledproximately to uncover the spacer 10 connected to the instrument 80.Once in position, the second assembly 104 is inserted into theinstrument 80 and is rotated to begin the deployment of at least one ofthe superior arm 14 and inferior arm 16 or both simultaneously. FIG. 15b illustrates the superior arm 14 and the inferior arm 16 in a partiallydeployed position with the arms 14, 16 rotated away from thelongitudinal axis. Rotation of the driver 104 turns the actuator shaft50 advancing it with respect to the body 12 which distally advances theactuator 48 whose bearing surfaces 58 contact the superior and inferiorcamming surfaces 41, 43 pushing the superior and inferior arms 14, 16into rotation about the pins 40. The position of the arms 14, 16 in FIG.15 b may be considered to be one of many partially deployedconfigurations or intermediary configurations that are possible and fromwhich the deployment of the arms 14, 16 is reversible with oppositerotation of the second assembly 104.

Turning to FIG. 15 c , there is shown an insertion instrument 80connected to a spacer 10 in a first deployed configuration in which thearms 14, 16 are approximately 90 degrees perpendicular to thelongitudinal axis or perpendicular the initial undeployed configuration.Continued rotation of second assembly 104 threads the shaft 50 furtherdistally with respect to the body 12 of the spacer 10 pushing thebearing surfaces 58 further against the superior and inferior cammingsurfaces 41, 43. While in the first deployed configuration, theclinician can observe with fluoroscopy the positioning of the spacer 10inside the patient and then choose to reposition the spacer 10 ifdesired. Repositioning of the spacer may involve undeploying the arms14, 16 rotating them into any one of the many undeployed configurations.The spacer may then be re-deployed into the desired location. Thisprocess can be repeated as necessary until the clinician has achievedthe desired positioning of the spacer in the patient.

Even further advancement of the actuator shaft 50 via rotation of thesecond subassembly 104 from the first deployed configuration results inthe spacer 10 assuming a second deployed configuration shown in FIG. 15d . The second deployed configuration is an extended configuration inwhich the superior and inferior arms 14, 16 extend transversely withrespect to the longitudinal axis outwardly in the direction of thearrows in FIG. 14 c . Such extension is guided by the length and shapeof the slots 28 in which the arms 14, 16 move. Once deployed, thesuperior arm 14 seats the superior spinous process and the inferior arm16 seats the adjacent inferior spinous process. Such extension may alsoprovide some distraction of the vertebral bodies.

Following deployment, the second assembly 104 may be removed. Control114 is rotated in the opposite direction to release the body 12 from theinstrument 80. The insertion instrument 80, thus released from thespacer 10, is removed from the patient leaving the spacer 10 implantedin the interspinous process space as shown in FIG. 16 . In FIG. 16 , thespacer 10 is shown with the superior arm 14 seating the superior spinousprocess 138 of a first vertebral body 142 and the inferior arm 16seating the inferior spinous process 140 of an adjacent second vertebralbody 144 providing sufficient distraction to open the neural foramen 146to relieve pain. As mentioned above, the shape of the superior arm 14 issuch that a superior concavity or curvature 45 is provided to conform tothe widening of the superior spinous process 138 in an anteriordirection toward the superior lamina 148 going in the anteriordirection. In general, the superior arm 14 is shaped to conform toanatomy in the location in which it is seated. Likewise, as mentionedabove, the shape of the inferior arm 16 is such that an inferiorconvexity or curvature 47 is provided to conform to the widening of theinferior spinous process 140 in an anterior direction toward theinferior lamina 150. The supraspinous ligament 152 is also shown in FIG.20

The spacer 10 is as easily and quickly removed from body of the patientas it is installed. The instrument 80 is inserted into an incision andreconnected to the spacer 10. The shaft 50 is rotated in the oppositedirection via a driver 104 to fold the arms 14, 16 into a closed orundeployed configuration. In the undeployed configuration, the spacer 10can be removed form the patient along with the instrument 80 or, ofcourse, re-adjusted and re-positioned and then re-deployed as neededwith the benefit of minimal invasiveness to the patient.

Any of the spacers disclosed herein are configured for implantationemploying minimally invasive techniques including through a smallpercutaneous incision and through the superspinous ligament.Implantation through the superspinous ligament involves selectivedissection of the superspinous ligament in which the fibers of theligament are separated or spread apart from each other in a manner tomaintain as much of the ligament intact as possible. This approachavoids crosswise dissection or cutting of the ligament and therebyreduces the healing time and minimizes the amount of instability to theaffected spinal segment. While this approach is ideally suited to beperformed through a posterior or midline incision, the approach may alsobe performed through one or more incisions made laterally of the spinewith or without affect to the superspinous ligament. Of course, thespacer may also be implanted in a lateral approach that circumvents thesuperspinous ligament altogether as well as in open or mini-openprocedures.

Other variations and features of the various mechanical spacers arecovered by the present invention. For example, a spacer may include onlya single arm which is configured to receive either the superior spinousprocess or the inferior spinous process. The surface of the spacer bodyopposite the side of the single arm may be contoured or otherwiseconfigured to engage the opposing spinous process wherein the spacer issized to be securely positioned in the interspinous space and providethe desired distraction of the spinous processes defining such space.The additional extension of the arm(s) subsequent to their initialdeployment in order to seat or to effect the desired distraction betweenthe vertebrae may be accomplished by expanding the body portion of thedevice instead of or in addition to extending the individual extensionmembers 14, 16.

The extension arms of the subject device may be configured to beselectively movable subsequent to implantation, either to a fixedposition prior to closure of the access site or otherwise enabled orallowed to move in response to normal spinal motion exerted on thedevice after deployment. The deployment angles of the extension arms mayrange from less than 90 degrees (relative to the longitudinal axisdefined by the device body) or may extend beyond 90 degrees and remainstationary or be dynamic. Each extension member may be rotationallymovable within a range that is different from that of the otherextension members. Additionally, the individual superior and/or inferiorextensions 42 a, 42 b, 44 a, 44 b may be movable in any directionrelative to the strut or bridge extending between an arm pair orrelative to the device body in order to provide shock absorption and/orfunction as a motion limiter, or serve as a lateral adjustmentparticularly during lateral bending and axial rotation of the spine. Themanner of attachment or affixation of the extensions to the arms may beselected so as to provide movement of the extensions that is passive oractive or both. In one variation, the saddle or distance betweenextensions 42 a and 42 b or between 44 a and 44 b can be made wider toassist in seating the spinous process and then narrowed to secure thespinous process positioned between extensions 42 a and 42 b or between44 a and 44 b.

The preceding merely illustrates the principles of the invention. Itwill be appreciated that those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the invention and are included withinits spirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

We claim:
 1. A spacer, comprising a body; a first arm having a distalend and a proximal end opposite to the distal end and attached to thebody; a second arm having a distal end and a proximal end opposite tothe distal end and attached to the body; and an actuator assemblycoupled to the body, the actuator assembly comprising a threaded shaftconfigured to rotate relative to the body and an actuator coupled to thethreaded shaft and configured to move laterally as the threaded shaft isrotated, the actuator comprising two opposing bearing surfacesconfigured to respectively engage and move the distal ends of the firstand second arms away from each other as the threaded shaft is rotated ina first direction.
 2. The spacer of claim 1, wherein the first andsecond arms are configured for rotation with respect to the body.
 3. Thespacer of claim 1, wherein each of the first arm and the second armcomprises a bridge and two extensions extending from the bridge andconfigured to engage a one of a first vertebra or a second vertebra whenthe spacer is disposed between the first and second vertebrae and thethreaded shaft is rotated in the first direction.
 4. The spacer of claim1, wherein the body comprises a plurality of notches defined therein andconfigured for attachment to prongs of an insertion instrument.
 5. Thespacer of claim 1, wherein the actuator assembly is configured to movethe distal ends of the first and second arms toward each other as thethreaded shaft is rotated in a second direction, opposite the firstdirection, after the first and second arms have been moved away fromeach other.
 6. The spacer of claim 1, wherein the threaded shaftcomprises a socket configured for engagement by a drive element of aninsertion instrument for rotating the threaded shaft using the driveelement.
 7. The spacer of claim 6, wherein the socket is a hex socket.8. A method for implanting a spacer, the method comprising: moving thespacer into a subject by inserting the spacer through a supraspinousligament of the subject to position the spacer directly between a firstvertebra of the subject and a second vertebra of the subject, whereinthe spacer comprises a body, a first arm attached to the body, and asecond arm attached to the body; and rotating, in a first direction, athreaded shaft that is coupled to the body of the spacer, wherein therotating laterally moves an actuator, which is coupled to the threadedshaft, relative to the body so that the actuator engages and moves thedistal ends of the first and second arms away from each other and intoengagement with the first vertebra and second vertebra, respectively. 9.The method of claim 8, further comprising rotating, in a seconddirection opposite the first direction, the threaded shaft to move thedistal ends of the first and second arms toward each other after thefirst and second arms have been moved away from each other.
 10. Themethod of claim 8, wherein the rotating comprises rotating the first andsecond arms with respect to the body.
 11. The method of claim 8, whereineach of the first arm and the second arm comprises a bridge and twoextensions extending from the bridge.
 12. The method of claim 8, furthercomprising attaching an insertion instrument to the body of the spacerprior to moving the spacer into the subject.
 13. The method of claim 12,wherein the attaching comprises engaging a plurality of notches definedby the body of the spacer using prongs extending from a distal end of ashaft of the insertion instrument.
 14. The method of claim 8, whereinthe rotating comprises engaging the threaded shaft with a drive elementof an insertion instrument to rotate the threaded shaft using the driveelement.
 15. The method of claim 14, wherein the engaging comprisesinserting a distal end of the drive element into a socket of thethreaded shaft.
 16. The method of claim 15, wherein the socket is a hexsocket.
 17. A kit, comprising the spacer of claim 1; and an insertioninstrument comprising a shaft having a distal end and a proximal end anda drive element extending along the shaft and configured to engage thethreaded shaft of the actuator assembly of the spacer and rotate thethreaded shaft in the first direction.
 18. The kit of claim 17, whereinthe body of the spacer defines notches therein and the insertioninstrument further comprises a plurality of prongs extending form thedistal end of the shaft and configured for engaging the notches.
 19. Thekit of claim 17, wherein the threaded shaft comprises a socketconfigured for engagement by a drive element.
 20. The kit of claim 19,wherein the socket is a hex socket.